Apparatus for separating magnetic susceptible particles



y 1954 P. E. CAVANAGH ETAL 3,133,015

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APPARATUS FOR SEP-ARATING MAGNETIC SUSCEPTIBLE PARTICLES Original FiledAug. 16. 1957 12 Sheets-Sheet 3 cu '0 N LA I f O l CD 8 3 \O o I i 2 f3r0 IO w, O N I co O O (\J (D r0 INVENTORS CARL w. HEDBERG 1 PATRICK E.CAVANAGH H BY WIJ vf/da ATTORNEYS y 1954 P. E. CAVANAGH ETAL 3,133,015

APPARATUS FOR SEPARATING MAGNETIC SUSCEPTIBLE PARTICLES Original FiledAug. 16. 1957 12 Sheets-Sheet 4 I N VENT ORS CARL W. HEDBERG PATRICK E.CAVANAGH BY flM 7, ,JM

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APPARATUS FOR SEPARATING MAGNETIC SUSCEPTIBLE PARTICLES Original FiledAug. 16, 1957 12 Sheets-Sheet s INVENTORS CARL W. HEDBERG E. GAVANAGH BYHMZ'W ATTORNEYS y 1964 P. E. CAVANAGH ETAL 3,133,015

APPARATUS FOR SEPARATING MAGNETIC SUSCEPTIBLE PARTICLES 12 Sheets-Sheet8 Original Filed Aug. 16. 195'? INVENTORS CARL W. HEDBERG BY PATRICK ECAVANAGH .wwm

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APPARATUS FOR SEPARATING MAGNETIC SUSCEPTIBLE PARTICLES Original FiledAug. 16. 1957 12 Sheets-Sheet 9 ATTORNEYS M y 12, 1 4 P. E. CAVANAGHETAL 3,133,015

APPARATUS FOR SEPARATING MAGNETIC SUSCEPTIBLE PARTICLES l2 Sheets-Sheet10 Original Filed Aug. 16. 1957 INVENTORS CARL W. HEDBERG PATRICK ECAVANAGH /mcwn AM ATTORN EYS May 12, 1964 P. E. CAVANAGH ETAL ,133,

APPARATUS FOR SEPARATING MAGNETIC SUSCEPTIBLE PARTICLES Original FiledAug. 16. 195'? l2 Sheets-Sheet 11 324 VENTORS RL w. HEDBERG CK E.GAVANAGH BY flM E' 7 ATTORNEYS May 12, 1964 P. E. CAVANAGH ETAL3,133,015

APPARATUS FOR SEPARATQING MAGNETIC SUSCEPTIBLE PARTICLES Original FiledAug. 16, 1957 12 Sheets-Sheet 12 INVENTORS CARL w. HEDBERG BY PATRICK E.CAVANAGH ATTORN EYS United States Patent 3,133,015 APPARATUS FORSEPARATING MAGNETIC SUSCEPTIBLE PARTICLES Patrick E. Cavanagh,()airville, Ontario, Canada, and Carl W. Hedberg, Bound Brook, N.J.,assignors to Research- Cottrell, Inc, Bridgewater Township, N.J., acorporation of New Jersey Original application Aug. 16, 1957, Ser. No.678,468, now Patent No. 2,990,124, dated June 27, 1961. Divided and thisapplication Feb. 13, 1961, Ser. No. 94,107

6 Claims. (Cl. 209-39) This invention relates to a new and improvedapparatus for separating and concentrating magnetic susceptiblematerials.

It is a particular object of the present invention to provide apparatusfor a system for concentrating magnetite bearing low grade ores toprovide a premium ore containing 60% or better iron content.

It is a particular object of the present invention to provide apparatusfor carrying the system into operation which is principally adapted forconcentrating low grade iron-containing minerals having relatively highmagnetic attractabilities such as magnetite (Fe O Franldinite(FeMnZn)O.(FeMn) O ilmenite (FeT O and the like. These minerals haveappreciably higher magnetic attractabilities than, for example, thefeebler magnetic susceptible iron-containing minerals such as hematite 23)- These and other objects and advantages of the present invention areprovided by a magnetic separator for air suspended particles including afirst cylindrical drum, means axially mounting the drum for rotation ina generally horizontal plane, means for rotating the drum about theaxial mounting, a second cylindrical drum having a diameter less thanthe diameter of the first drum, a plurality of permanent magnets securedto the outer surface of the second cylindrical drum in a spiral arrayincluding leftand right-hand spirals to form a generally herring-boneconfiguration, means for mounting the second cylindrical drum forrotation within the first cylindrical drum, means for rotating thesecond cylindrical drum to provide a differential speed between thefirst and second drums, means for directing air suspended particulatematerial including magnetic susceptible particles to the outer surfaceof the first cylindrical drum, means for collecting magnetic susceptibleparticles adjacent the edges of the first cylindrical drum where theattractive force of the magnetic field is reduced, and means adjacentthe collecting zone for directing a stream of pressure fluid in adirection opposite the direction of travel of the magnetic susceptibleparticles.

These and other objects and advantages of the present invention willbecome more apparent to those skilled in the art from the followingdetailed description of the present invention which will be morecompletely described with reference to the accompanying drawingswherein:

FIG. 1 is a vertical view of the magnetic separation apparatus adaptedfor treating the fine fraction of ground material;

FIG. 2 is a top plan view of the magnetic separator shown in FIG. 1;

FIG. 3 is a section substantially on line 33 of FIG. 2;

FIG. 4 is a vertical, sectional view through the fine fraction feedmechanism for the separator shown in FIG. 1;

FIG. 5 is a section substantially on line 55 of FIG. 4;

FIG. 6 is a section substantially on line 66 of FIG. 3;

FIG. 7 is a section substantially on line 77 of FIG. 3;

FIG. 8 is an enlarged fragmentary view of the structure shown in FIG. 7;

ice

FIG. 9 is a top plan view of one of the rotor members of one of themagnetic separator shown in FIG. 1;

FIG. 10 is an end view of one of the magnetic separatorson line 1010 ofFIG. 7;

FIG. 11 is a similar view of one of the separators substantially on line11-11 of FIG. 7;

FIG. 12 is a diagrammatic sectional view showing the flow path ofmaterial through a portion of the separator shown in FIG. 1;

FIG. 13 is a view similar to that shown in FIG. 12 taken at right anglesthereto;

FIG. 14 is an enlarged fragmentary sectional view of the permanentmagnets for the magnetic separator units of the device shown in FIG. 1;

FIG. 15 is a fragmentary view of the means for attaching the magnets tothe unit shown in FIG. 14;

FIG. 16 is a fragmentary view of the attaching system shown in FIG. 15;

FIG. 17 is a top plan view of attaching means for connecting the innerends of the permanent magnets on a separator of the type shown in FIG.1;

FIG. 18 is asection substantially on line 1818 of FIG. 17;

FIG. 19 is an enlarged view of one of the magnet units of the separatorshown in FIG. 1;

FIG. 20 is another view of the permanent magnet shown in FIG. 19; and

FIG. 21 is a top plan View of the magnet shown in FIGS. 19 and 20.

Referring particularly to FIGS. 4 and 5 an air stream carrying asuspended fine fraction of ground ore in conduit 46 enters housing 186within which is maintained a plurality of cyclone separators generallydesignated 182. In the form of the apparatus shown in the drawings about32 separators are employed in each of the separation units 48. Thecyclone separators comprise a plurality of separator tubes 184 which aresupported in a horizontal header sheet 186 extending across the housing180. Within each of the separator tubes 184 is maintained an outlet tube188 of lesser diameter than the separator tube 184. The lower end ofeach outlet tube 188 projects into the interior portion of itscomplementary separator tube while the upper end projects through anupper header sheet 190 where anchoring means 192 are provided. At theinlet to the separator tubes 184 are provided spinner rings 194 whichinclude a plurality of spinning vanes 196. The vanes 196 extend betweenthe outer surface of the outlet tube 188 and the inner surface of theseparator tube 184 whereby the gas stream carrying the suspendedparticles to be separated into the space between the lower header sheet186 and the upper header sheet 190 is caused to swirl upon entering intothe interior portion of the separator tubes 184.

The gas stream containing the suspended particles induced to swirl bythe vanes 196 continues in a swirling path downwardly into the separatortubes 184. Centrifugal force developed by the swirling gas stream causesthe suspended particles to concentrate in the portion of the gas streamadjacent the inner surface of each of the separator tubes 184. A portionof the gas stream entering each of thetubes and the major part of thesuspended particles leaves the separator tubes adjacent the lower outlet198 into a collection chamber generally designated 2%. The remainder ofthe gas stream passes upwardly through the outlet tubes 188 of each ofthe centrifugal separators and in passing from each separator tube intothe outlet tubes the gases flow about helical straightening vanes 202which convert the energy of rotation of the gases to kinetic energy andreduce the pressure loss which would otherwise take place in themechanical cyclone separators 182. The gas stream leaving the outlettubes 188 3 collects in upper plenum chamber 204 and then issues fromthe separator units 48 through suitable discharge conduits as disclosedin our Patent 2,990,124.

In general it has been found that removal of 90% of the suspending airpermitting only of the air to pass with the fine fraction to theseparators 34 has been found to give very satisfactory results. Forexample, where 30 cubic feet of air is required to suspend each pound offine fraction of ground material, the volume of air is decreased tothree cubic feet per pound of dust prior to the passage of the finefraction through the helical magnetic separators, and satisfactoryresults are obtainable when from about 80 to about 95% of the suspendingair stream is removed at this point.

The primary portion of the fine fraction of ground material along with apredetermined portion of the suspending air stream issuing into theplenum chamber 280 move downwardly about grids or baffles 266 and 208.As shown in FIGS. 12 and 13 the grids or bafiles 266 and 288 aid in theequal distribution of the gas stream and its suspended particles intothe plural magnetic separators 210 in the uppermost horizontal row ofthe magnetic treating units 48. From separators 210 the material movesto further magnetic separator units designated 216' and 210" which as tobe more fully described are identical in form to separator units 210.

Each parallel layer 210, 210', and 216" of separators includes 4parallel rows as more clearly shown in FIG. 2 and designated 212, 214,216 and 218.

Each of the magnetic separators 212 through 213 in each layer 210, 210'and 210 are identical, in form and operation, in each of thesubstantially vertical rows. It will also be apparent that separators212 of layers 210, 21% and 210" may be considered as a unit as materialtreated in the uppermost unit is serially treated by the units 212 ofthe next lower rows 210 and 210". It will also be seen from FIGS. 1 and3 that each parallel layer 210, 210' and 210" of separators is providedwith a complete drive unit designated 220, 220', 228", 222, 222' and222" respectively.

Referring particularly to FIGS. 7, 8, 9, 10 and 11, a single magneticseparator will now be described. These separators comprise an outercylindrical drum having a substantially cylindrical deck 224 and heads226 and 227. The deck 224 is preferably constructed of stainless steeland the drum heads 226 and 227 are preferably constructed of aluminumwith plastic inserts 229 to prevent establishment of eddy currents. Drumhead 226 is rotatably mounted on shaft 228 by anti-friction bearings230. The other head 227 is also rotatably mounted on shaft 228' byanti-friction bearing 232. Drum head 227 also includes an extensionportion 234 which has secured thereto a pair of cog wheels or sprockets236.

The cog wheels 236 of each layer 210 to 210 and 210" are driven by driveunits 220, 220 and 220".

Each drive unit 220, etc. comprises an electric motor 238 connected to aconventional adjustable speed reducing mechanism 240 having an outputshaft 242 to which is secured a cog wheel 244 which drives the pluralsprockets 236 of each drum 224 through endless chains 246 maintainedwithin drive chain housings 248 as more clearly shown in FIG. 2 of thedrawings.

The outer surface of each drum deck 224 is divided into 4 sectionsdesignated 258, 252, 254 and 256 by cylindrical sleeves 258 which mayhave upturned peripheral ends 268. The peripheral edges of adjoiningcylindrical battles are in abutting relationship.

Within each of the drums 224 is rotatably mounted an inner drumgenerally designated 262, each drum 262 comprising a cylindrical shell264 and drum heads 266 and 268. Drum head 266 is keyed to rotate withshaft 228 while drum head 268 is keyed to rotate with shaft 228'. Theouter ends of shafts 228 and 228 are rotatably secured in bearings 270and 272 at the respective ends of the separator units.

Between bearing 270 and 230 of shaft 228 are keyed a pair of cog wheelsor sprockets 274, similar to sprockets 236 which drive the outer drum224. Sprockets 274 are driven by drive units 222, 222 and 222 in each ofthe plural layers through motors 276, variable speed reduction means 278having output shaft 280 which has keyed, to the extended end thereof, asprocket 282 for driving endless chains 284 maintained within housing286 enclosing the plural sprockets 274 in each of the plural layers ofseparator units.

Each of the inner drums 264 of the separators 48 has secured thereabouta plurality of permanent magnets 290. The form of the magnets 2%, theattaching means therefor and their arrangement on the drum deck will bemore particularly described with reference to FIGS. 7, 8, 9 and 14through 21.

Each inner drum 264 comprising one layer and designated 259, 252, 254and 256 has arranged on the outer surface thereof four groups of magnets290 designated 292, 294, 2% and 2%. Each of these groups is identical inform and arrangement and the detailed description of arrangement 292will also apply to the remainder of the group. Magnetic group 292comprises two sets of plural magnets 36%) and 362. The plural magnets inset 300 are positioned upon the outer surface of drum deck 264 in agenerally spiral arrangement and the plural magnets in set 362 arepositioned upon the drum deck in a reverse spiral arrangement so thatthe magnets of sets 300 and 362 cooperate to define a generallyherring-bone configuration as best shown in FIG. 9 of the drawings. Withthe drum 264 rotating in the direction of directional arrow 384 of FIG.9, the helically arranged magnets in sets 300 and 302 urge magneticsusceptible particles deposited on the outer surface of bathe 258secured to the outer drum deck 224 to move toward the flared ends 266,in a direction away from the center line 306 of the collecting group292. As more clearly shown in FIGS. 7 and 9, as the magnetic susceptibleparticles migrate toward the extended ends of the upturned baffies 260the particles are progressively moved further from the magnetic fieldcreated by the plural magnets 290 and into collection zones formed byplural vertically extending bafiles 368 from which the magneticsusceptible particles are discharged to collect in hoppers beneath theunits 48 as to be more fully described hereinafter.

Adjacent baffles 368 form collection troughs 310 which intersect thedrum adjacent the space between successive separation zones 292, 294,296 and 29 8.

In order to provide the generally helical or herringbone configurationof the magnetic field in each of the collecting units the magnets 290are preferably of U-shaped configuration in cross-section havingextended pole faces 312 and 314. The elongated U-shaped magnets 290 arealso curved or warped to conform to the outer surface of the inner drum264 at their lower face 316 as more clearly shown in FIGS. 19 and 20while the upper surface comprising pole faces 312 [and 314 are shaped toconform generally to the shape of the inner surface of the outer drumdeck 224 when the magnets are secured to the inner drum deck 264 in agenerally helical array. Since each of the magnets 296 is a segment of ahelix upon the drum deck 264 the ends 3 18 and 320 of the magnets arecut at an angle to the longitudinal axis of the magnet whereby each endface 218 and 220 is parallel to a radial plan through the drums.

The outermost units of magnets adjacent the drum heads 266 and 268 aresecured to the drum deck 264 by bolts 322 having threaded ends 324 whichpass through a band of non-magnetic material such as aluminum 326, thedrum deck 264, and a portion of the drum heads 266 or 268 as the casemay be. A nut and lock washer 328 secures the threaded ends of the bolts322 to complete the assembly. The remote ends of each of the bolts 322are bent at generally right angles to the longitudinal axis of the boltsas at 336 which curved end is adapted to fit into the space 332 betweenthe legs of the U-shaped magnets as more clearly shown in FIGS. 15 and16 of the drawings. In order to prevent interference with the mag neticfield the bolts 322 are preferably constructed of non-magnetic material.The opposed ends of the magnets 290 of each unit 300 and 302 areconnected together by means of a generally H-shaped clamping bar 334with the legs 336 of the bars 334 extending into the spaces between thepole faces 312 and 314 of opposed pairs of magnets. A clamping screw 338threadedly engages a tapped bore 340 in the drum deck whereby oneclamping bracket 334 and one bolt 338 maintains the opposed ends of 4Ushaped magnets 290 to the deck 264. A nonmagnetic band 342 extendsbeneath the ends of the magnets and the clamping brackets 334 toeliminate eddy currents in the assembly. The opposed ends of the magnetsof each separation set 250, 252, 254 and 256 for each drum 264 areclamped by a bracket 344 of FIG. 7 similar to brackets 334 only thewidth of the bar portions 346 of the brackets 344 are wider than thecorresponding bar portions of brackets 334 to accommodate for the largerspacing between the magnets comprising the plural separating sections.

While the magnets 290 for the magnetic separators 48 have been describedas having a generally U-shaped configuration in cross-section it will beapparent that elongated bars, rods or discrete magnetic blocks may besubstituted therefor without departing from the scope of the presentinvention. In the preferred form of the present invention U-shapedmagnets have been shown and described as the use of U-shaped magnetssimplifies the attaching of the magnets to the outer surface of theinner drums 264.

The flow path of particles through separators 48 and the collection ofmagnetic and non-magnetic particles therein will be described withreference to FIGS. 1, 2, 3, 5, 6 and 7.

The fine particles of material suspended in the air stream entering theeylone type separating units through conduit 46 pass out the lower ends138 of each of the separators along with about 5-10% of the suspendingair stream. The particles and about of the suspending air stream enterthe plenum chamber 200 below the mechanical separator units where theair stream and the particles are divided into a plurality of smallerstreams by baffles 208 and 206 more clearly shown in FIG. 6 of thedrawings. Fro-m baffles 208 and 206 the air stream and the suspendedparticles flow past the upper tier of rotating drums 212, 214, 216 and218. The outer surface of the magnetic separators are rotated in thedirection of the directional arrows shown, for example, in FIG. 3. Inpassing the surfaces of the outer drums 224, the magnetic susceptibleparticles are held against the sleeve 258 and due to the helical form ofthe magnetic fields created by the helically arranged magnets 290,secured to the outer surface of the inner drum 264, the magneticsusceptible particles are urged to move towards flared ends 260 of saidsleeves. In passing across the surface 258 of the sleeves to the flaredends 260 the magnetic particles pass under partition members 308 whichform pass-ages 310 for the magnetic susceptible particles. Once theparticles are within the spaces 310 formed by the bafiles 308 theparticles are out of the major flow of gas through the separator and arecaused to move away from the magnetic fields created by magnets 290 bythe slope of the baflies as at 260. As the particles move further awayfrom the magnetic fields they fall into the plural hoppens 360positioned below the lowermost tier of drum type separators. Theparticles of magnetic susceptible material collect in hoppens 360 forfurther treatment or disposal.

As the magnetic susceptible particles pass the sleeves 258 an opposingcurrent of air aids in maintaining a clean separation between themagnetic and non-magnetic particles. The opposing stream of air isconveyed into each tier of rotating drums through a header 217, 217' and217" providing a plurality of off-take pipes 219 which directs the airinto the plural passages 221 between each vertical tier of separators.The air forced into passages 221 flows into the concentrate conduits 310through openings 223, all as more clearly shown in FIG. 2 and FIG. 6 ofthe drawings.

The non-magnetic materials and those having very weak magneticattractabilities pass over the surface of the drum and are depositedupon the drums of the next lower tier where further concentration takesplace. The magnetic susceptible materials removed from the stream againenter confined passageways 310 and the non-magnetic materials arecarried by the air stream to the next lower rotating drums. Thenon-magnetic materials leaving the lowermost tier of drums pass into thespaces 362 interposed between the concentrate conveying passages 310. Inpassing through the spaces 362 to the lower end of the non-magneticmaterial receiving hoppers 364 the carrier gas stream is withdrawnthrough an air draw-01f system generally designated 366.

The air stream draw-off system generally comprises an off-take pipe 368more clearly shown in FIGS. 3 and 6 connected to a source of reducedpressure created, for example, by a fan. Gas drawn through the conduits368 creates a zone of lower pressure in chamber 366 whereby the airstream containing the non-magnetic particles within the passages 362 iscaused to pass through louver sections 370 which communicate with aportion of the passages 362 as shown in FIG. 6. The louvered passages370 are constructed of a plurality of overlapped louvers or turningvanes 372 which are so positioned that the air stream in passing betweenthe plural louvers is caused to turn sharply. In turning past the edgesof the louvers 372, the particles of non-magnetic material suspended inthe air stream are thrown outwardly and downwardly into the lower end ofthe hoppers 364 from which they pass through suitable conduits.

From the conduits the substantially non-magnetic materials may bedisposed of or directed to further magnetic separators.

The air stream withdrawn from plenum chamber 366 through conduit 368 maybe passed through a conventional gas cleaning system.

It has been found that very satisfactory separation is brought about inseparators 48 when the diameter of the outermost drums 224 is from about8 to about 18 inches and the innermost drum rotates in the oppositedirection in close proximity to the inner surface thereof. It will beappreciated that the speed of the drums and their diameters and thestrength of the magnetic fields created by the plural magnets 290 areall interdependent so that if the speed of rotation of the drums isincreased or the diameter of the drums are decreased the field strengthof the magnets must be increased.

With the separator units wherein the outer drum is from about 8 to about18 inches in diameter satisfactory results are obtained when the outerdrum is rotated at from about 25 to about 200 rpm, the inner drum isrotated in the opposite direction at from about 50 to about 400 r.p.m.,and the magnetic field created by the magnets is from about 700 to about1000 gauss at the surface of the outer drum 224.

With this arrangement of magnetic field strength, drum diameters andspeeds of rotation satisfactory operation and separation of particles inthe range of from about l50 to about +325 mesh containing from about 10to 40% of 325 mesh particles.

From the foregoing description, it will be seen that the presentinvention provides a new and useful means for concentrating low grademagnetic susceptible iron ores that fully accomplishes the aims andobjects hereinbefore set forth.

This application is a division of our co-pending applica- 7 tion SerialNo. 678,468 filed August 16, 1957, now United States Patent 2,990,124issued June 27, 1961.

We claim:

1. A magnetic separator for air suspended particles comprising a firstcylindrical drum, means axially mounting said drum for rotation in agenerally horizontal plane, means for rotating said drum about the axialmounting, a second cylindrical drum having a diameter less than thediameter of the said first drum, a plurality of permanent magnetssecured to the outer surface of said second cylindrical drum in adjacentright and left hand arrays of helical segments, means for mounting saidsecond cylindrical drum for rotation within said first cylindrical drum,means for rotating said second cylindrical drum to provide adifferential speed between the first and second drums, means fordirecting air suspended particulate material including magneticsusceptible particles to the outer surface of said first cylindricaldrum, means for collecting magnetic susceptible particles adjacent theedges of said first cylindrical drum where the attractive force of themagnetic field is reduced, and means adjacent said collection Zone fordirecting a stream of pressure fiuid in a direction opposite to thedirection of travel of the magnetic susceptible particles.

2. A magnetic separator for air suspended particles comprising a firstcylindrical drum having outwardly flared peripheral edges, means axiallymounting said drum for rotation in a generally horizontal plane, meansfor rotating said drum about the axial mounting, a second cylindricaldrum having a diameter less than the diameter of said first drum, aplurality of substantially U-shaped permanent magnets secured to theouter surface of said second cylindrical drum in adjacent right and lefthand arrays of helical segments with the legs of said U-shaped magnetsdirected toward the inner cylindrical surface of said first drum, meansfor mounting said second cylindrical drum for rotation within said firstcylindrical drum, means for rotating said second cylindrical drum toprovide a differential speed between the first and second drums, meansfor directing air suspended particulate material including magneticsusceptible particles to the outer surface of said first cylindricaldrum, means for collecting magnetic susceptible particles adjacent theflared edges of said first cylindrical drum where the attractive forceof the magnetic field is reduced, and means adjacent said collectionzone for directing a stream of air in a direction opposite to thedirection of travel of the magnetic susceptible particles.

3. The invention defined in claim 2 wherein said U- shaped magnetscreate a magnetic field of from about 700 to about 1000 gauss.

4. A permanent magnet for a magnetic drum separator comprising anelongated magnet having a generally U- shaped configuration incross-section, said U-shaped magnet being warped into a segment of ahelix defined on the outer surface of a magnetic drum.

5. The invention defined in claim 2 wherein the means for directing airsuspended particulate material to the outer surface of said firstcylindrical drum includes a plurality of cyclone type gas suspendedparticle separating means, each of said particle separating means havinga gas suspended particle inlet, an outlet for a portion of the particlesuspending gas, and a concentrated particle and gas outlet, each of saidconcentrated particle and gas outlets positioned to discharge generallyvertically above the upper surface of said first cylindrical drum,whereby the particulate material suspended in a portion of a gas streamdirected to the cyclone type gas suspended particle separating means isdirected toward the upper surface of said first cylindrical drum.

6. The invention defined in claim 5 including means for removing theremainder of the particle suspending gas below said magnetic separator.

References Qited in the file of this patent UNITED STATES PATENTS528,055 Williams Oct. 23, 1894 2,144,184 Hale et al. Jan. 17, 19392,711,249 Laurila June 21, 1955 FOREIGN PATENTS 401,301 Great BritainApr. 4, 1932 376,458 Italy Nov. 15, 1939 968,015 France Nov. 4, 1953

1. A MAGNETIC SEPARATOR FOR AIR SUSPENDED PARTICLES COMPRISING A FIRSTCYLINDRICAL DRUM, MEANS AXIALLY MOUNTING SAID DRUM FOR ROTATION IN AGENERALLY HORIZONTAL PLANE, MEANS FOR ROTATING SAID DRUM ABOUT THE AXIALMOUNTING, A SECOND CYLINDRICAL DRUM HAVING A DIAMETER LESS THAN THEDIAMETER OF THE SAID FIRST DRUM, A PLURALITY OF PERMANENT MAGNETSSECURED TO THE OUTER SURFACE OF SAID SECOND CYLINDRICAL DRUM IN ADJACENTRIGHT AND LEFT HAND ARRAYS OF HELLICAL SEGMENTS, MEANS FOR MOUNTING SAIDSECOND CYLINDRICAL DRUM FOR ROTATION WITHIN SAID FIRST CYLINDRICAL DRUM,MEANS FOR ROTATING SAID SECOND CYLINDRICAL DRUM TO PROVIDE ADIFFERENTIAL SPEED BETWEEN THE FIRST AND SECOND DRUMS, MEANS FORDIRECTING AIR SUSPENDED PARTICULATE MATERIAL INCLUDING MAGNETICSUSCEPTIBLE PARTICLES TO THE OUTER SURFACE OF SAID FIRST CYLINDRICALDRUM, MEANS FOR COLLECTING MAGNETIC SUSCEPTIBLE PARTICLES ADJACNT THEEDGES OF SAID FIRST CYLINDRICAL DRUM WHERE THE ATTRACTIVE FORCE OF THEMAGNETIC FIELD IS REDUCED, AND MEANS ADJACENT SAID COLLECTION ZONE FORDIRECTING A STREAM OF PRESSURE FLUID IN A DIRECTION OPPOSITE THEDIRECTION OF TRAVEL OF THE MAGNETIC SUSCEPTIBLE PARTICLES.